Commit 9f8681db authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[DCCP] ccid3: Shift window counter computation 



 This puts the window counter computation [RFC 4342, 8.1] into a separate
 function which is called whenever a new packet is ready for immediate
 transmission in ccid3_hc_tx_send_packet.

Justification:

 The window counter update was previously computed after the packet was sent. This has
 two drawbacks, both fixed by this patch:
   1) re-compute another timestamp almost directly after the packet was sent (expensive),
   2) the CCVal for the window counter is needed at the instant the packet is sent.

Further details:

 The initialisation of the window counter is left in the state NO_SENT, as before.
 The algorithm will do nothing if either RTT is initialised to 0 (which is ok) or if
 the RTT value remains below 4 microseconds (which is almost pathological).

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
parent de553c18

net/dccp/ccids/ccid3.c

+29 −20
Original line number Diff line number Diff line
@@ -161,6 +161,33 @@ static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len) 
	 */

}



/*

 * 	Update Window Counter using the algorithm from [RFC 4342, 8.1].

 * 	The algorithm is not applicable if RTT < 4 microseconds.

 */

static inline void ccid3_hc_tx_update_win_count(struct ccid3_hc_tx_sock *hctx,

						struct timeval *now)

{

	suseconds_t delta;

	u32 quarter_rtts;



	if (unlikely(hctx->ccid3hctx_rtt < 4))	/* avoid divide-by-zero */

		return;



	delta = timeval_delta(now, &hctx->ccid3hctx_t_last_win_count);

	DCCP_BUG_ON(delta < 0);



	quarter_rtts = (u32)delta / (hctx->ccid3hctx_rtt / 4);



	if (quarter_rtts > 0) {

		hctx->ccid3hctx_t_last_win_count = *now;

		hctx->ccid3hctx_last_win_count	+= min_t(u32, quarter_rtts, 5);

		hctx->ccid3hctx_last_win_count	&= 0xF;		/* mod 16 */



		ccid3_pr_debug("now at %#X\n", hctx->ccid3hctx_last_win_count);

	}

}



static void ccid3_hc_tx_no_feedback_timer(unsigned long data)

{

	struct sock *sk = (struct sock *)data;
@@ -333,6 +360,8 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb) 
		 */

		if (delay - (suseconds_t)hctx->ccid3hctx_delta >= 0)

			return delay / 1000L;



		ccid3_hc_tx_update_win_count(hctx, &now);

		break;

	case TFRC_SSTATE_TERM:

		DCCP_BUG("Illegal %s state TERM, sk=%p", dccp_role(sk), sk);
@@ -353,7 +382,6 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len) 
	const struct dccp_sock *dp = dccp_sk(sk);

	struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);

	struct timeval now;

	suseconds_t quarter_rtt;

	struct dccp_tx_hist_entry *packet;



	BUG_ON(hctx == NULL);
@@ -373,25 +401,6 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len) 
	}

	packet->dccphtx_tstamp = now;

	packet->dccphtx_seqno  = dp->dccps_gss;

	/*

	 * Check if win_count have changed

	 * Algorithm in "8.1. Window Counter Value" in RFC 4342.

	 */

	quarter_rtt = timeval_delta(&now, &hctx->ccid3hctx_t_last_win_count);

	if (likely(hctx->ccid3hctx_rtt > 8))

		quarter_rtt /= hctx->ccid3hctx_rtt / 4;



	if (quarter_rtt > 0) {

		hctx->ccid3hctx_t_last_win_count = now;

		hctx->ccid3hctx_last_win_count	 = (hctx->ccid3hctx_last_win_count +

						    min_t(unsigned long, quarter_rtt, 5)) % 16;

		ccid3_pr_debug("%s, sk=%p, window changed from "

			       "%u to %u!\n",

			       dccp_role(sk), sk,

			       packet->dccphtx_ccval,

			       hctx->ccid3hctx_last_win_count);

	}



	hctx->ccid3hctx_idle = 0;

	packet->dccphtx_rtt  = hctx->ccid3hctx_rtt;

	packet->dccphtx_sent = 1;

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